How Does an HVAC System Work? All You Need to Know

What actually is an HVAC system? How many different types are there? How Does an HVAC System Work?

Most people know what HVAC stands for: Heating, Ventilation, and Air Conditioning, and most homeowners have a basic understanding of the purpose of an HVAC system and how it works.

Yet, not too many people understand everything that goes into an HVAC system, which can be an issue when you need to troubleshoot your existing HVAC system or when you need to purchase a new one.

After all, with so many HVAC products available in the market, choosing the right one for your needs can be quite a daunting task, and it would pay to know what’s what.

In this guide, we will discuss the basics of the HVAC system and how it works, and by the end of this guide, you’d have learned about:

• What is an HVAC system?
• How an HVAC system works
• Important parts and components of an HVAC system
• How to troubleshoot an HVAC system

And more.

Let’s begin this guide with the basics: what is an HVAC system?

What Is an HVAC System?

As discussed, HVAC stands for Heating, Ventilation, and Air Conditioning. 

An HVAC system is, simply put, a piece of equipment or a collection of equipment that can provide three different functions: 

1. Providing a source of warm air (heating)
2. Distributing air, typically through ducts or pipes (ventilation)
3. Providing a source of cool air (cooling or air conditioning)

Thus, an HVAC system is a system that regulates and moves either heated or cooled air throughout a building, both residential and commercial.

There are also HVAC systems with a fourth function: refrigeration, and so it’s often called HVAC/R or HVAC-R.

HVAC-R systems are more often found in commercial rather than household settings.

There are also HVAC systems that can control humidity levels in a building, as well as improve air quality by incorporating filters and air cleaners that can capture bacteria, viruses, and spores.

How Does an HVAC System Work?

While there are many different models of HVAC systems available with different technologies used, they all work on the same principle: taking in the fresh air, cooling or heating the air using a mechanical ventilation system, then distributing the cooled/heated air throughout the building.

To achieve such function, there are three main components of an HVAC system:

1. A source of cool air (condenser or heat pump) and/or a source of warm air (mainly a furnace)
2. A control unit (i.e., a thermostat) to regulate the whole system
3. A distribution system, mainly ducts or pipes

An HVAC system can cool fresh air with either a condenser or a heat pump.

A condenser is a conventional air conditioning unit that collects warm air from inside the building and moves it outside. A condenser does not actually cool the fresh air and distribute it, but rather it takes the warmer air away from the building.

On the other hand, a heat pump both heats and cools the air (contrary to its name.) When needed to cool the air, it works with a similar principle to a condenser. However, when you want to warm up the air inside the building, it works in reverse: pulling warmer air from outside the building and then distributing it inside the building.

Meaning, that if the HVAC system has a condenser and not a heat pump, it will need to rely on a furnace for heating purposes.

However, there are HVAC systems that have both heat pumps and furnaces, which is called a double HVAC system.

Other Components of an HVAC System

While this won’t be an exhaustive list of components and equipment within an HVAC system, here are the most important ones that can help you better understand how they work, as well as a basic understanding of each of these components: 

1. Air Return

The air return draws air into the main system through the filters.

2. Air Exchanger

An air exchanger exchanges stale or for fresh air, allowing the air inside the building to stay cleaner (reducing particles, allergens, etc., ) and may also help control humidity.

3. Air Filter

Most HVAC systems and, especially furnaces, utilize air filters between 1-4 inches in diameter. These filters trap debris and particles that enter the HVAC system. 

Eventually, these filters will get clogged and need to be cleaned or changed regularly.

4. Evaporator Coils and Coolant

Important parts of condensers (AC units) and heat pumps.

The coolant, or cooling agent, is responsible for cooling the pumped air. Older AC units use Freon as the coolant, which is considered bad for the environment. However, newer units use Puron, which is more environmentally friendly. 

The evaporator coils’ main job is to cool the coolant so that unless there’s a leak in the coolant’s storage, it will remain cool, and you’ll never run out of the coolant agent. These coils technically absorb and transfer heat (and moisture,) and the size can vary depending on the efficiency of the HVAC unit.

5. Vent and Ductwork

Ducts carry and distribute the air to various places around the building, while vents or registers provide an opening for the air so the cooled/heated air can be distributed to the building.

There are many different types of ducting systems available, and some may not be compatible with certain heat pumps or AC units. If you plan to purchase a new HVAC system, it’s important to evaluate its compatibility with your existing ducts.

6. Exhaust Outlets

Referring to any components or areas where heat is vented from the building. Chimney flues are a good example of exhaust outlets.  

7. Thermostat

A thermostat allows users to adjust and control the temperature of air distributed by the HVAC system. In practice, the thermostat relays instructions throughout the system, which can be very complex and involve multiple communications with various devices in the system.

There are many different types and models of thermostats available in the market, including smart thermostats that can be automated. 

Several electrical inputs may be needed in the thermostat, depending on the complexity of your system.

8. Compressor

Another crucial part of a condenser (AC unit) or heat pump. A compressor is responsible for regulating the pressure of the coolant. A compressor requires regular maintenance to avoid technical issues.

How Does an HVAC System Work: Heating

Most HVAC systems rely on the use of furnaces to heat the building.

There are many different types of furnaces available based on the fuel sources used, and here are the major types:

• Natural gas furnaces: the most widely used type of furnace in North America, natural gas furnaces are very effective in providing even heating throughout the en tire building. However, they are relatively expensive, especially when compared to oil or electric furnaces. 
• Oil furnaces:  an oil furnace is a cost-effective option, and you can expect it to cost around 25% less compared to a comparable natural gas furnace. However, the tradeoff is oil furnaces aren’t as efficient as natural gas furnaces (around 10-20% less efficient.)
• Electric furnaces: electric furnaces use electric components to transfer heat to the circulated air. They are more portable than natural gas furnaces, but they are also less efficient. Another key advantage is that electric furnaces have better longevity and can last roughly ten years longer than both oil and natural gas furnaces. 
• Propane furnaces: not very popular, only used in about 10% of US households, propane furnaces can be just as effective and efficient as natural gas furnaces, but you’ll need to change the propane tank more often. A great alternative if your home doesn’t have access to the natural gas pipeline.
• Modulating furnaces: as efficient as natural gas furnaces but as cost-effective as the oil or electric furnace. However, modulating furnaces requires a more significant investment upfront, although it will save you money in the long run. A modulating furnace modulates a continuous flow of gas rather than shutting the furnace on and off, making it more efficient in energy consumption.

Besides the furnace, most HVAC systems also use blower motors, which distribute the heated air throughout the building through its ductwork, which is known as the forced-air system.

A heat pump can technically heat a building by absorbing heat from outside the building and moving it inside. 

However, due to how it works, a heat pump won’t be very efficient when heating a building at very cold temperatures outside (freezing temperatures and below.) While the heat pump will still be able to absorb and move ambient heat from the outside, typically, it won’t be sufficient. 

This is why most HVAC systems with heat pumps tend to pair them with an electric furnace to supplement the heat pump’s heating function. 

How Does an HVAC System Work: Cooling

Most HVAC systems include either a condenser (air conditioner) unit or a heat pump to perform “cooling.”

As discussed above, “cooling” here doesn’t actually mean the condenser will cool the air around it, but rather will absorb and move warm air from within the building and move it to the HVAC system’s outdoor unit that is vented into the atmosphere. 

By moving the heat from the building, it will technically “cool” the air inside the building.

In practice,(air conditioner unit), this process is achieved by the component called coolant (or often called refrigerant.)

Coolants like Freon or Puron can be liquid or gaseous in form, depending on air pressures. The HVAC system modulates the pressures of the coolant depending on the needs of the system and where the coolant is. 

The coolant would absorb ambient heat and then would remove the heat by changing form at a different pressure while moving from inside the system to outside. 

This process happens continuously, over and over, with the coolant’s pressure modulating to systematically remove the warm air and the ambient heat from the building.

A condenser can only move ambient heat from inside to outside the building. Yet, a heat pump can do the reverse to absorb ambient heat from the outside and transfer it inside the building for heating purposes.

How an HVAC System Performs Ventilation or Distribution

Besides heating or cooling a building temperature, another key function of an HVAC system is to ventilate the building by distributing air throughout it. The HVAC system mainly distributes air via ductwork or vents.

Most HVAC systems will also include a vent stack or chimney flue for discharging heat (which is also essential for cooling purposes.) 

If the HVAC system uses a furnace to heat the building, it’s crucial to understand that even the most efficient furnace won’t have 100% of its energy going towards heating the building, and some of the energy must be vented outside the building. The best furnaces in the market, however, can reach 97% of efficiency, meaning only 3% of energy is dissipated back.

Some buildings may also add additional ventilation to allow air to escape on the side of the building instead of exclusively above them. This design is quite common in newer HVAC systems, which can help prevent moisture condensation in the HVAC system. Continuous moisture buildup may damage the HVAC system.

Maintaining and Troubleshooting Your HVAC System

Due to the complexity and potential risks of installing and servicing an HVAC system, most states in the US require that only certified contractors that have completed sufficient training can perform installations, part replacements, and major repairs of HVAC systems.

However, simpler troubleshooting like changing air filters can be performed by homeowners or other non-certified people.

Not only does installing and servicing an HVAC system require extensive skill sets and experience across various fields (i.e., plumbing, electrical work, metalwork, etc.,) many of the installation and parts replacement processes would require specialized and often expensive equipment.

With that being said, if you’re looking to install an HVAC system in your house or looking to repair your existing HVAC equipment, we’d recommend getting professional and certified help.

Cocoon Home Services provides you with an easy way to get help for installing or servicing your HVAC system with just a single tap, click, or phone call. Sign up with Cocoon today, and we’ll send a Cocoon ServicePro to help with your HVAC system and maintenance right away.